This invention relates to methods and devices for surface mounting pins and other components with male projections to a substrate such as a printed circuit board.
The two major ways that components are attached to printed circuit boards (PCBs) are with boards that have holes in them, and boards without holes. In boards with holes typically produced by through-hole drilling or punching, a component, i.e., pin, tab, resistor, etc., is inserted via its projecting male terminal or terminals into the hole in the board and the component is held in place by an interference fit, clinch, or a spring form on a component leg. After all the components are attached, the components are subsequently wave soldered to the PCB. A problem arises that through-hole drilling or punching is associated with a relatively large hole size tolerance, which also increases the solder pad on the PCB that surrounds the hole. As boards get smaller and smaller, this hole and pad size take up too much room on the board.
In boards without holes the components are surface mounted. In this case, the pads on the surface mount board are printed (silkscreen or stencil) with solder paste and the components are placed on these solder printed pads and then the solder is reflowed. The great advantage in surface mount is that there is a potential real estate board savings of up to 70% of the area of the board.
Typical surface mount components such as resistors, capacitors, Ics, are low to the board. This means that the aspect ratio (height to width) of the component is small.
A problem arises when a tall or high aspect ratio component, i.e., test point, connector pins, relay package, needs to be surface mounted. To simply solder or re-flow a test point or pin component, besides being difficult, does not result in a very sturdy structure. Hence, the surface mounted component in field use can easily be broken off during a mating or mishandling operation. Presently, manufacturers solve this problem by having a hybrid (mixed technology) board where the components are both mounted in holes as well as surface mounted. The problem with this is that the boards become more costly with the addition of the holes and some of the real estate savings are lost. Also, separate assembly machines to insert surface mount and through-hole components are required.
Reference is also made to the above-mentioned related application, whose contents are incorporated herein by reference. That application describes machine surface mounting pins and pin headers using a conventional pick and place machine. The pins are constructed with a relatively large base so that a sturdier mounting to the PCB solder pad is obtained. That application also describes the use of special pin holders for holding the pins in pockets in a plastic tape supplied from a reel, with the pick and place machine using a vacuum or suction head to pick a component and place it, manually or as directed by a computer, into its proper place on the PCB, for subsequent soldering. The special holder not only makes it easier to use suction to pick-up the pin and transport it to the PCB, but also helps support the pin until soldered in place. Alternatively, if no holder were used, grippers could be used on the pick and place machine to lift the pin and transport it to the PCB.
A disadvantage of the schemes described in the copending application is that a pin insertion machine cannot be used to assemble the pins to the surface mounted PCB. Also, the shank of the pin is too long for many standard pick and place machines (already in service) to vacuum pick up the pin. In addition, the packaging of the pin in tape and reel format typically results in a pocket in the plastic tape that does not position the pin with sufficient accuracy for the vacuum pick up nozzle. As described in the 1989 article referenced in the related application and entitled "Six (6) Easy Enhancements of Continuous Pin and Post Terminals", delivered at the Sep. 25-28, 1989 Coil Winding Proceedings Meeting at O'Hare Exposition Center, Rosemount, Ill., whose contents are also incorporated herein by reference, known pin inserter machines are capable of high speed and high production rates. Not being able to use a conventional pin inserter machine increases substantially the cost of producing populated PCBs.